The Initial Attach document discusses procedures for initial attach by a user attaching to an LTE network for the first time, as defined as EMM Case No. 1 in our previous document, “Eleven EMM Cases in an EMM Scenario”. The document consists of two companion documents: this document (Part 1. Cases of Initial Attach) and the subsequent document (Part 2. Call Flow of Initial Attach). In this document, we will distinguish different cases of initial attach (Attach Case 1 ~ Attach Case 5), and different function blocks involved in each case. Then we will explain different procedures required in each case of initial attach. In the subsequent document, detailed initial attach procedures in Attach Case 1 will be described.

This document discusses initial attach, as defined as EMM Case 1 in our previous document, “Eleven EMM Cases in an EMM Scenario” [1]. During this phase, a user turns on his device (UE) for the first time after subscribing to an LTE network/service, and attempts to attach to the network, sending an IMSI to the network (The initial procedure will be the same if the user is using an IMSI as his UE ID, even when he has previously attached to the network).

The initial attach procedure may vary depending on circumstances. It can be as in EMM Case 1, to be explained below, or as in EMM Case 11 (initial attach in another city), to be covered in the subsequent document later. Or it can be other types depending on whether or not a user (UE) kept the information used for his last attach to the network (hereinafter referred to as the “Last Attach Information1, or whether the network (MME) has information about the user, including UE ID, (hereinafter referred to as the “Last UE Context”2). So, this document (Part 1 of Initial Attach) will describe different initial attach types, and find out their characteristics and differences from one another. The subsequent document (Part 2) will focus on EMM Case 1, providing the related procedures in details.

This document is organized as follows:

Chapter 2 identifies different initial attach cases, and

Chapter 3 briefly discusses different initial attach procedures of each case, by listing the functions to be performed by MME.

I have been an xDSL/GPON/Ethernet/IP System Architect for the past 15 years and recently I started to work on LTE.During one of my searches on detailed LTE information I came accross your site.Looking at your papers and presentations, I must admit I never saw more detailled drawings than yours !Congratulations for those who created them !

I wonder which software package are you using ?I'm a regular Microsoft Visio user but IMO this package falls short for this kind of drawings ..

Netmanias2013-12-31 15:55:57

Hello Mr. Dirk Van Aken,

Thanks for having interest in our site.

Most of our diagrams were created using Microsoft Visio. And we didn't use any special SW package. While providing professional consulting services in various technical fields over 10 years, we have created quite a lot of Visio templates ourselves.

Sincerely, Netmanias.com

Paulos Rizos2014-01-02 18:11:13

Top quality as always, really appreciating these english versions. Looking forward to the next technical document.

Boonchai2014-03-18 16:37:55

Excellent Thank you

Boonchai2014-03-18 16:38:25

Excellent Reference to understand

ASHOK2014-04-04 22:04:23

Very nice and easy to understand...

ASHOK2014-04-04 22:04:52

Very nice and easy to understand.. and more informative as well

Naresh Babu2014-06-26 20:38:02

This is what I need to understand call flows. Finally I am in right place.

tuan2014-08-07 18:48:38

thanks you

vipin garg2014-10-01 14:57:33

Hi Netmanias,

Thanks for these excellent explanations. Recently I cleared an interview in which your tutorials played a major role. :)

I think, the scene ii) the MME doesn’t have the valid Last UE Context of the UE can cover the scene iv) the UE was detached from other MME last time.

Kendy Nowax2015-04-03 19:00:44

Thanks for this material.

Very helpful and easy to understand. Hope that you will upload some material about AS side.

Ayaz mohammed2015-07-02 21:26:38

Thanks Alot....

Nice and simple..Please share more documents on LTE..

Ritzmond M. Josef2015-07-12 23:23:10

Very informative... Thanks a lot netmanias.com. Keep it up!

Tony Lee2015-09-22 07:13:58

Your material is great! A good introdution before one dive into 3gpp spec

aleksandar2016-02-27 14:32:18

Hello,

Do you maybe have call flow for the following case:

1.Subscriber is attached to 2-3G network.

2.Subscriber is not provisioned on HSS

3.Subscriber is using LTE capable phone.

Subscriber has active 2-3G PDP session. What is the scenario when UE attempts to handover to 4G in this case? Can Modify Bearer request from MME to SGW happen before successfull ULR/ULA (that obviously can not be successfull, as subscriber is not provisioned in HSS)?

Thank You!

prahladbutola2016-03-05 21:31:34

In a very simple way the subject is explained nicely...

AnnaG2016-04-27 03:01:49

Very good documentation. Easy to understand and to the point.

Had a question- Figure 2 Attache case 3. If the NAS security setup is already done with OLD MME, when the UE attaches to the new MME, How can the new MME process these messages and contact the old MME ? Wont the integrity check fail as the integrity setup of the UE was with old MME and not the new MME ?

santosh.patra2016-06-24 12:16:23

Very useful and easy to understand the flow end to end...Kudos to the team.

Thank U.

chamod2019-09-17 15:02:20

Man who is uploading this contain deservers a nobel ;-)

Mahmood2019-10-29 01:22:08

Thank you for breaking down the call flow into easy to understand steps supported with beautuful visuals

May Allah guide you to the ultimate truth.

Fahd Ali Khan2020-01-15 23:22:30

Need IMS end to end call flow..

MRawat2020-02-19 18:32:06

Dear Netmania Team,

If new MME sucessfully identified old MME , then how Old MME not able to provide UE identity to New MME. As per this scenario UE previously attached to Old MME and must have UE identifucation. Pls let me know what causes "Identification Response (error cause)"

The UE requests for initial attach using its Old GUTI. So, the MME (New MME) asks the Old MME for the Last UE Context relating to the UE, but fails to receive any. So, the MME requests the UE for a UE ID, and acquires an IMSI.